WORKSHOP SERIES ON HYDROPOWER
Important news and update
Francis-99 data moved here (permanent archive)
Background
Hydropower plays a critical role to meet global energy demand in the category of the renewable energy. Hydropower is also valuable for achieving the targets of the United Nations Sustainable Development Goals (mainly 6, 7 and 13). In recent years, hydropower faces new challenge on flexible energy demand. The turbines are often operated at unfavorable load, which has raised significant concerns for the operating life of a turbine. In order to adapt new requirement, robust design and analysis tools and techniques are needed. Computational fluid dynamic (CFD) techniques have been widely used for turbine design and flow analysis. However, the numerical tools and techniques require proper verification and validation with experimental data. Furthermore, the numerical modelling of hydro turbine is time consuming and expensive due to involved complexities, high Reynolds numbers, flow separation, secondary flow, cavitation, losses, etc. Thus, a simplified and low cost solution is valuable for the hydropower industry. Availability of high quality experimental data and reference design is valuable to overcome both challenges of numerical modelling. Due to confidentiality, none of the modern turbine designs and data are available in public domain. This makes it difficult for researchers to explore their skill and knowledge in numerical modelling.
Francis-99 is a collection of workshops offering open access to scientific data on specific test cases, including Francis turbines and hydrofoils. This data is available for researchers to verify and validate their computational fluid dynamic and fluid-structure interaction models. To date, three workshops have been conducted successfully. The first focused on the steady-state operating conditions of a Francis turbine. The second addressed transient operating conditions, such as load variation and start-stop. The third workshop focused on fluid-structure interactions in Francis turbine and hydrofoil. The hydrofoil test case provided high quality validation of the data with natural frequency and the particle image velocimetry.
Waterpower Laboratory outside view.
Experimental facility
The Francis-99 workshop series is initiated and and managed by the Waterpower laboratory (NTNU). The experimental data are provided by the laboratory. The Waterpower laboratory is actively involved in research and development of hydro turbines since 1917. It consists of a state-of-the-art infrastructure, which gives the possibility to operate test rigs in various configurations mimicking prototype situations. The laboratory is equipped with two important test rigs, Francis turbine/pump-turbine and Pelton turbine, capable of conducting experiments according to international standard (IEC 60193). Achieved hydraulic efficiency of the model Francis turbine is 93.4%. There are small other rigs to carry out measurements for the basic research, for example, hydrofoil rigs in three distinct configurations, single hydrofoil, linear cascade of three hydrofoils, radial cascade of eight hydrofoils. The conduit system can be pressurized up to 100 m head. Available pumping power is 700 kW and the maximum flow rate is 1.1 m3 s-1. The laboratory is upgraded regularly with state-of-the-art equipment; the initial upgrade was carried out in 2003 and 2007. Turbine generator, conduit system and flow measuring instruments have been upgraded most recently in 2023. The Francis-99 rig is the featured test facility at the Waterpower laboratory.
Francis-99 turbine and draft tube.
The model Francis turbine available in the Waterpower laboratory, also known as Francis-99 turbine, is a scaled (1:5.1) model of the turbines operating at Tokke power plant in Norway. The Francis turbine is a splitter blade type runner consisting of 15 blades and 15 splitters (short blades). The leading edge profiles of the blades and splitters are similar. The blades are twisted upto180 degree along the chord length from inlet to the outlet of the runner. The blade thickness at the trailing edge is around 3 mm. Runner inlet and outlet diameters are 0.630 m and 0.349 m, respectively. The obtained hydraulic efficiency during model tests in 2012 was 93.4% at the best efficiency point and the uncertainty was +/- 0.16% [1]. The test rig is extensively used for the other studies, such as rotor stator interaction, vortex rope, rotating stall with pump-turbine runner, water hammer, cavitation, etc. The open loop hydraulic system is widely used to perform transient measurements, such as load variation, start-stop, and total load rejection. This model turbine has played important role in the research and development of the high head turbines over the last decade globally.
Francis-99 outlet and blade trailing edge.
Highlight of the first workshop
The first workshop was organized on 15 -16 December 2014 at the Norwegian University of Science and Technology. Experimental data (including blade loading) at steady state operating conditions of the Francis-99 runner were provided. Several researchers have conducted extensive numerical studies on the on the given test case, and the obtained good quality results. The researchers presented the numerical results with proper verification and validation during the workshop. Approximately 50 researchers participated in the workshop, and 14 papers were presented. Almost all aspects of numerical studies were discussed during the workshop including numerical modelling, meshing, verification and validation, challenges in the numerical study, and how can numerical modelling be optimized. The presented papers were published in Journal of Physics: Conference Series, Volume 579.
Highlight of the second workshop
The second workshop was organized on 14 - 15 December 2016 at Norwegian University of Science and Technology. Total 10 research papers were presented in the workshop. Around 35 researchers from different countries were participated in the workshop. Both steady and transient simulations results were presented and discussed during the workshop. For the transient simulation, mesh deformation approach was used. Key concern was long simulation time during load variation and start-stop. There was alternative suggestion to use 1D-3D coupling that allow reduction of time. Main components of the turbines can be modelled using 3D and data from 1D analysis should be used as boundary condition. Further, size of the 3D CFD domain can be reduced by using passage modelling approaches as highlighted in the first workshop. Results presented from the hydropower industries indicated that modern passage-modelling techniques should be used which allow rough estimation of pressure loading on the blades during load variation and start-stop. Results presented using different techniques/solvers such as Ansys, star-ccm+, OpenFOAM have shown that newly implemented techniques can help to overcome the challenges in transient modelling and can provide results with improved accuracy. The presented papers were published in Journal of Physics: Conference Series, Volume 782.
Highlight of the third workshop
The third workshop was organized on 28 - 29 May 2019 at Norwegian University of Science and Technology. This workshop aimed at fluid structure interactions in a Francis turbine. However, in this workshop, two test cases were provided: (1) Hydrofoil and (2) Francis turbine. The hydrofoil test case aimed to investigate fundamental research, and the turbine test case aimed to investigate applied research. Parameters such as study of mode-shape, nodal-diameter, deformation, fatigue loading, estimation of fatigue life, individual/combined natural frequencies, hydrodynamic damping, harmonic response, etc. were investigated. Total 11 papers were submitted to the workshop and around 35 participants from different countries, Canada, Spain, Germany, Croatia, Sweden, North Macedonia, Norway, etc., joined the workshop. This was the last workshop of the first three scheduled workshops however, there was large interest to continue the workshop series with high quality data from the laboratory measurements. There are several unknown questions relating to the hydro turbine and numerical modeling. Significant progress has been made in robustness of the numerical modelling in recent years. But, there are open question on the accuracy and trust on numerical results, more specifically on the fluid structure interaction in hydro turbine. The next series of the Francis-99 workshop will be announced when experiments on other test cases are completed in the Waterpower laboratory. The presented papers were published in Journal of Physics: Conference Series, Volume 1296.
